It's not atmospheric pressure, it's internally induced pressure due to buoyancy differences, which are normally created due to gravity and a connection that is rigid enough to withstand the internally induced pressure. If you have a closed system of two non-rigid containers connected by a rigid body, then the fluid will try to flow in the direction of its buoyancy. Helium balloons connected internally by a straw (even a curvy one) would try to fill the higher balloon, right?
So yeah, he's right that in the absence of gravity, a normal siphon will not work. But, if you took that siphon system on the ISS and put one end outside in space, and one inside, you'll have a siphon-like effect due to air pressure. Likewise, if you take two balloons of water with a rigid connector and submerge one in a pool of Hg, then that "siphon" will work against gravity.
I'm non-union and involved in installing new machines in a union business. They require us to hire union people to do the installation while we are restricted to supervision. So they do indeed do that.
As for higher wages across the board? Unions these days are pretty self-serving, even amongst their own. Thus you get two-tier wage levels or even three or four tiers in some cases. The older guys won't vote in lowering their $30/hr operator wages, so they cut more from the new guys who aren't voting yet, who end up getting around $14/hr with minimal increases.